Mate a face or line to a focal point

james_howard360

I'm trying to model a camera that is always pointed at a focal point regardless of camera location. This was super easy in Solidworks, just mate an axis in the camera to the focal point in the assembly. I've tried every mate type in OnShape and no joy. Any idea how this can be done?

SethF

This might not be ideal, because you end up with an extra part in your assembly. You can make it transparent and really small, and even hide it, but it'll still be there. Here's the basic run down:

1) make a small part in addition to your camera
2) use a ball mate to connect the small part to your focal point (in my example, its the origin).
3) use a cylindrical mate to connect the camera to small part.

You can check out my example here:
https://cad.onshape.com/documents/505e3e366881a7854a2191de/w/fde742db20aedd854e57576b/e/9dfea2692a8b4bfffb23721a

Hope that helps!

John_P_Desilets

@james_howard360 I did something similar to @SethF. I just used construction geometry and ball mates. 

https://cad.onshape.com/documents/8697bade0f1804af31a85a39/w/7cdec442cc978762199ed942/e/582ab8e1898586fdf0184144

james_howard360

Both of these solutions almost get there. Both require the distance between the objects to be static, however, and I need the distance to vary. @John_P_Desilets yours gave me the clue: I added a single sketch with a construction circle and used three mates like so: circle [ball mate] focal point, circle [parallel] face of camera, circle [cylindrical mate] camera lens axis. It's a bit slow to solve but otherwise works great. Thanks for the layup.

SethF

Interesting that you couldn't get either of them to work with varying distances.. On my end I can move the camera anywhere. I wonder if it had something to do with the way mates are prioritized when you're freely moving stuff around an assembly.




But I'm glad you got what you needed! I haven't done a lot with Assemblies, so I don't think I had ever used construction geometry within an assembly. So thank you @John_P_Desilets and @james_howard360 for showing me that!